, Blue Ink wrote

*snip*

That's not likely to happen, I'm afraid. With an average daily insolation of 6 kWh/m2 ; even a sedan designed in the '70s would be way too small.

Not to mention that the sun is, by definition, a variable source: you must have a way to store large amounts of energy somehow. 

Cheap, light, non-polluting, large capacity batteries is the nut we need to crack; once we get there, the energy source becomes less relevant.

MIT is working on nano-battery technology, they've applied for a patent anyway. I wonder how they're doing?